4th Gear

My '92 XJ 4.0 does something odd in 4th gear... it's an automatic by the way...anyway when I shift into 4th gear my rpm sstay fairly high for a few seconds and then drop down suddenly to where it should be. I figure, if this is supposed to happen, that it happens to give me extra power that I otherwise wouldn't have at the low end of 4th gear? Anyway, I just want to make sure this isn't going to destroy my engine so let me know if you have any ideas or knowledge about this.

Maybe you are noticing the engagement of the lockup torque converter. At 35 in normal mode or at 45 in power mode at relatively light throttle, the torque converter will lock. Give it a little more go pedal and the lockup will release again. The drop would be about 10-15% I think- it is on other vehicles I have owned- I do not have a tach on my XJ. If the rev up happens during the 3-4 upshift, something is wrong.

Mine started doing that just prior to a TPS failure. It started with the high rpms in fourth and progressed down. After a couple of days I found myself running 3500 rpm trying to get it to shift out of first. The good news is that a new TPS is about $40 and only takes to 2 bolts to change. It is surprisingly easy to swap out, especially for a Jeep :laugh: If you have a voltmeter you can check the input/output readings to see if it’s bad. BTW a bad TPS doesn’t always throw an engine code, mine didn’t. I misplaced my records so I can’t give you the voltage readings right now, but FSM, Hynes, or Chilton’s has it. Or you can do a search here; lots of people have replaced their TPS :laugh3:

I go with the torque converter lock-up theory. The transmission has four speeds, but when the TC locks up in 4th it feels like shifting to another gear and the RPMs drop noticeably. It's supposed to do that -- you worry when it DOESN'T lock up.

Thanks, actually I replaced my TPS fairly recently and it's been doing this all along with the new one, unfortunately I never drove it when the old TPS was functional so I dont know if that's it.

My 99 does the same thing. When it shifts out of third into fourth the rpms go down and if I'm not on the gas or goin up a hill they will drop again. I was worried that something was slipping. Anyway I've always been paranoid about it and let off so it will shift all the way. So it isn't hurting anything?

mine does the same thing even after a new TPS but the thing is the TC doesnt unlock